For the purpose of removing particulates, such as NOx and particulate matter, generated in an exhaust gas with the driving of the internal combustion, in particular, the diesel internal combustion, there has been known an exhaust gas after-treatment apparatus in which a catalyst converter that oxidizes and burns carbon hydride in an exhaust gas is combined with a particulate filter that traps particulates, so that combustion of the particulates trapped in the particulate filter is promoted with the use of heat generation in the catalyst converter (JP-A-8-42326).
Incidentally, the catalyst converter of this type fails to exert the desired effect unless it is activated by being heated to a certain temperature. Hence, as is disclosed in JP-A-8-296485, there is known a method by which whether the catalyst is in an activated state is determined, for example, by detecting the temperature of the catalyst, and when the catalyst is determined to be in an inactivated state, an additional fuel injection, a so-called secondary fuel injection, is performed into the cylinder at specific timing later than the original combustion injection timing for the catalyst to become activated.
The control of the post fuel injection in the related art, however, is to promote the activation of the catalyst when the catalyst is determined to be in an inactivated state by injecting fuel into the cylinder intermittently at specific timing after the retain injection in an amount meeting with the driving condition of the engine, the external environmental condition, and so forth at that point in time.
No problem occurs in a case where the driving condition of the engine, the external environmental condition, and so forth remain the same to some extent. However, under the driving environment where these conditions vary in a relatively drastic manner, the activation of the catalyst is not promoted as expected even by the post fuel injection, and fuel is consumed wastefully after all. This method therefore has a problem that it becomes a large cause of deterioration in fuel consumption and it rather increases environmental pollution by emitting a large amount of unburned fuel together with the exhaust gas.
An object of the invention is therefore to provide an improved exhaust gas after-treatment apparatus capable of solving the problems in the related art discussed above.
Another object of the invention is to provide an improved exhaust gas after-treatment apparatus capable of achieving appropriate post fuel injection control.